National Water Commission

The Hobart water supply area is in the south east of Tasmania and for the purpose of the water balance is defined as the Derwent Estuary-Bruny surface water management area (1,104 km²). This excludes the majority of the physical Derwent water catchment which comprises the Upper and Lower Derwent River WMAs as well as the Derwent Estuary-Bruny WMA.

The Department of Primary Industries and Water (DPIW) is the licensing authority and manages both surface and groundwater diversions for urban, commercial/industrial, irrigation and environmental purposes. Hobart Water manages the major storages and protects the water quality in Hobart for bulk water supply. They also treat the bulk water and deliver it to local governments for distribution.

The majority of Hobart’s water supply comes from outside of the catchment. The supply network contains six major water storages within the WMA and a further two storages in the neighbouring Upper and Lower Derwent River WMAs. Within Derwent Estuary-Bruny, there are a number of creeks that drain into the estuary. The largest river totally contained within the WMA is the North West Bay River which flows from the south side of Mount Wellington to North West Bay (DPIWE, 2005a). The Derwent and Jordan Rivers both flow into and through the WMA but the majority of the water in these rivers is sourced from outside the WMA and are fed by runoff in the WMA. In the water balance the flows from the Derwent and Jordan Rivers are portrayed as a transfer in and out. The Derwent River itself is highly regulated downstream of Lake Meadowbank. The tidal limit in the Derwent River is about 1 km upstream of the New Norfolk Bridge in the Lower Derwent WMA.

Hobart Water supplies water from five major sources; just over half is drawn from the Derwent River from below Lake Meadowbank (operated by Hydro Tasmania), 15% from Lake Fenton, 20% from Hobart Mountain (Mount Wellington), 10% from the Southern Regional Supply and 2% from Glenorchy Mountain (Mount Arthur). This water is used to supply councils within the Hobart area and also to the Jordan and Pittwater-Coal water management areas and off-peak direct supply to the South East Irrigation Scheme. The supplies from Lake Meadowbank, Lake Fenton and the Southern Regional Supply constitute transfers into the WMA (Hobart Water, 2005). Hydro Tasmania release 20 cumecs from Lake Meadowbank; this release meets environmental requirements and the needs of Hobart Water at the Bryn Estyn treatment plant.

Figure 2 shows the major dams and the water supply distribution network within the Hobart water supply area. 



Figure 1 Hobart water supply area locality map

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Hobart water supply area locality map (1.1 Meg)

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Figure 2 Hobart water supply area schematic map (Source: Hobart Water, 2006)

Related Water Management Areas

The links below provide access to similar reports.

Llandherne

Unincorporated Area - Central South East

Rainfall across the Hobart area was below average in 2004-05, at around 89% of long term average rainfall (see Table 1). The 10 year average was 98% of the long term average (Figure 3). Rainfall has no apparent seasonal bias (Figure 4). Streamflows at Snug Rivulet (gauge 5202) were 62% of long term average (Figure 5).

There were restrictions on the North West Bay River from 22/12/2004 to 04/02/2005 limiting Surety 3 diversions to 50% and a total ban on all Surety 5 diversions. Water use has been steady with population since a jump in 2001-02 (Figure 6).

Table 1 Summary of Hobart water supply area contextual information

Figure 3 Annual rainfall for the Hobart water supply area (modified from BOM, 2006)




Figure 4 Monthly rainfall and evaporation for the Hobart water supply area (modified from BOM, 2006 & Climate Atlas)




Figure 5 Streamflow hydrograph for the Hobart water supply area at Snug Rivulet (gauge 5202)




Figure 6 Total water supplied by Hobart Water to Hobart compared to population from 1999-2000 – 2004-05 (source: WSAA, 2005)

Summary of the total water resources in the basin

The total volumes of water available and supplied from water resources in the Hobart area are shown in Table 2.

Table 2 Summary of water balance for the Hobart water supply area, 2004-05

 

Note: Except for Hobart water storages, opening and closing surface water storage volumes were based on storage capacities recorded for DPIW (i.e. assumed to be 100% full). Hobart Water was able to supply actual volumes for their storages.

Figure 7 Water balance summary diagram for the Hobart water supply area

Outcomes from the water cycle report

The following information becomes apparent from Table 2.

• The total change in storage was not a complete figure as the change in storage in minor dams was not available. Hobart Water’s storage levels decreased during the course of 2004-05.
• The known volume of minor catchment or farm dams in the area was 3% of captured rainfall indicating that the minor catchment dams have little influence on water availability.
• The rainfall in 2004-05 was below average for most months (Figure 4).
• Hobart Water supply approximately 40,000ML of water each year to local councils and private users. The storages in the WMA are used generally as transfer storages and they only hold about 11,000 ML of water.
• Local Councils are responsible for domestic water supply in Hobart. In general domestic water use is not metered, at the Council’s discretion.
• The volume error in the water balance was -4% for the combined surface water and groundwater resource.
• The Hobart water balance was dominated by the transfers in and out of the Derwent River and, to a lesser extent, Jordan River flows. This was due to the location of the WMA, on the estuary of the Derwent River. Both rivers feed into the WMA and flow directly to the estuary. There are no gauges on the Derwent River in the WMA; the only open gauge in the WMA in 2004-05 was on the Snug Rivulet (5202).
• Water use was predominantly from surface water resources.
• Data could not be obtained for the following items in the water balance:
• Groundwater storage volumes (renewable and non-renewable) and water quality (saline or non-saline).
• There was very little quantitative information on groundwater and surface water connection in the Hobart area.
• The actual storage volume for water that was not managed by DPIW. For these storages it was estimated that the storages were 100% full at the start and end of the year.
• There was no quantitative information available on the losses from the system.
• Soil - unsaturated zone storage volumes
• Snowpack
• River channels storage volumes

Summary of data availability and reliability

The data for this water balance was highly variable (Table 3) with most of the surface water information obtained from estimates, whilst the groundwater information was less detailed and only covered part of the WMA.

The data for this water balance was predominantly category D, indicating that the majority of the data was of a low standard. However, about 42% of the fields had no information for them either due to them being not applicable (e.g. no snow so no snow pack value), or not available. The overall reliability for the catchment was ±71% (between a C and D rating).

Table 3 Summary of Hobart water supply area data reliability

This page provides a summary of the results of the National Framework for the Assessment of River and Wetland Health (FARWH) for Hobart water supply area.

Table 4 Results of the National Framework for the Assessment of River and Wetland Health (FARWH) for Hobart water supply area

Figure 7 Results of the National Framework for the Assessment of River and Wetland Health (FARWH) for Hobart water supply area

Note: The ranges associated with the graph are described below.

Score	Condition
0.0-0.2	severely modified
0.2-0.4	substantially modified
0.4-0.6	moderately modified
0.6-0.8	slightly modified
0.8-1.0	largely unmodified

See the National Framework for the Assessment of River and Wetland Health (FARWH) report on the Publications page for details on the assessment method.

This page provides high level performance indicators of water management for the Derwent Estuary-Bruny surface water management area (SWMA) based on information provided by the government of Tasmania. It provides answers to a range of questions of relevance to the National Water Initiative (NWI), specifically in relation to: Surface water management framework Water resources caps Surface water / groundwater interaction Surface  water sustainable yield Environmental water requirements Surface water diversions Surface water entitlements Protected terrestrial areas Please note that a dash means that either the data was not available, not provided or that the question was not relevant for a particular area. Surface water management area Derwent Estuary-Bruny Project ID TAS_SW_24 Size of surface water management area 1,104 km² NWC drainage division code 305 Drainage Division Tasmania State Tasmania Surface water management framework What is the status of the water management plan for this surface water management area? Statewide policy If a final or draft plan has been written, what year was it completed? - If a final or draft plan has been written, does it consider groundwater explicitly? - If yes, how is groundwater considered? Technical assessment - Management decisions - What percentage of the surface water management area is covered by the water management plan(s)? - Does your water plan specify water quality objectives to meet environmental and other public benefit outcomes? - Other items included in the management framework are: Metering program for this area - Effluent recycling - Climate change - Aquifer storage and recovery - Household rainwater tanks - Efficient irrigation systems - Other - Management plan available at: Water resource caps Has a cap been placed on surface water usage / abstraction in this surface water management area? Yes Is the cap an absolute limit to allocation or provisional limit? Provisional If there is a cap, what year was it implemented? 1995 If there is a cap, is it considered to represent the sustainable surface water yield? No The following water usage types are included/not included under the cap: Irrigation Included Urban supply Included Commercial / Industrial Included Minor catchment storages Included Minor on-stream storages Included Minor extracted water storages Included Stock and domestic Not included Mining / Oil and gas Included Forestry Not included Floodplain harvesting Included Drought supply Included Greywater use Included Effluent recycling Included Aquifer storage and recovery Included Does auditing of compliance with the cap occur? No Compliance report available at: Surface water / groundwater interaction Are surface water and groundwater managed as an integrated water resource in this surface water management area? No Reason or method: Integration has not been assessed Integrated management plan available at: Surface water sustainable yield The sustainable yield within this surface water management area for 2004/05 was: Sustainable yield not assessed ML The method used to determine the sustainable yield was: Sustainable yield not assessed Was the sustainable yield determined for the combined (i.e. surface water and groundwater) water? Sustainable yield not assessed Is the cap considered to be at or below the sustainable yield of surface water? Sustainable yield not assessed What is the level of entitlements relative to the sustainable yield? Sustainable yield not assessed Environmental water requirements Have environmental water requirements been determined for this surface water management area? Yes - complete coverage of water management area If yes, what year were they completed? 2001 For regulated areas, how much of the mean annual flow is not available for allocation and provided for the environment? (percentage of mean annual flow at locality of river regulation) - Are there formal environmental water provisions for regulated rivers? - If so, what method was used to determine environmental water provisions for regulated rivers? - For what percentage of the rivers are provisions made? 15% Maps illustrating which rivers have provisions available at: Do the environmental water provisions consider groundwater? No If yes, how? - Completed Environmental Flows Reports available at: Completed Environmental Flows Reports Surface water diversions The total surface water diversion in the surface water management area for 2004/05 was: <%DataBinder.Eval(Container.DataItem, "SSDVOLML_C", " {0} ML") %>   What percentage of surface water diversion is determined from metered data? 0 % What is the level of diversions relative to the sustainable yield? Unknown volumes or no data provided For surface water diversion that is NOT metered, how was the surface water diversion determined for 2004/05? Estimated from irrigated areas No Estimated from licence volume Yes Estimated from power usage for pumps No Estimated from models No Other - Surface water entitlements Entitlements for surface water are required/not required for the following usage types: Irrigation Required Urban supply Required Commercial / Industrial Required Minor catchment storages Required Minor on-stream storages Required Minor extracted water storages Required Stock and domestic Not required Mining / Oil and gas Not required Forestry Not required Floodplain harvesting - Drought supply - Greywater use - Effluent recycling - Aquifer storage and recovery - Other - Protected terrestrial areas Each of the following protection types cover a percentage of the surface water management area as detailed: Habitat/species management area 0.25 Managed resource protected areas 3.64 National park 2.12 Natural monument - Protected landscape/seascape - Strict nature reserve - Wilderness area - Total 6.01 Related links The links below provide access to similar data reports for groundwater management units (GMUs) that overlap this surface water management area (SWMA).

Unincorporated Area - Central South East

Llandherne

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